GB2026043A

GB2026043A - Annealing aluminium

Info

Publication number: GB2026043A
Application number: GB7923470A
Authority: GB
Original assignee: Daido Steel Co Ltd; Sumitomo Light Metal Industries Ltd
Current assignee: Daido Steel Co Ltd; Sumitomo Light Metal Industries Ltd
Priority date: 1978-07-15
Filing date: 1979-07-05
Publication date: 1980-01-30
Also published as: ES482492A1; DE2928460C2; JPS613867B2; GB2026043B; FR2436190B1; FR2436190A1; JPS5514838A; US4288261A; DE2928460A1; AU4875079A; AU524029B2; CA1122106A

Description

1

SPECIFICATION

Method for the heat treatment of aluminium strips The present invention relates to a method for the heat treatment of aluminium strips, the method comprising heating an aluminium strip while being passed through a heating zone, and then cooling the strip while being passed through a cooling zone, thereby applying heat treatment such as annealing to the aluminium strip.

In prior arts, in the case where an alumini- urn strip is subjected to heat treatment as mentioned above, the strip in a floating condition is permitted to pass through a heating zone and the cooling zone overcomes the antibuckling stress, there sometimes gives rise to wrinkles, in the aluminium strip, in parallel to the moving direction 30 thereof, in other words, longitudinal wrinkles 41, as shown in Fig. 12, resulting in a defective aluminium strip.

For the purposes of this Specification the term -aluminium strip- shall be taken to include a thin and lengthy band-like alumini um plate continuously rolled by a rolling mill.

The thickness of the aluminium plate is nor mally less than 3.5 mm, and the plate has 95 various widths.

According to the present invention, there is provided a method for the heat treatment of aluminium strip comprising the steps of pass ing an aluminium strip in a floating mode through a heating zone, and passing the alu minium strip from the heating zone in a floating mode through a cooling zone, charac terised by the step of curving, in a position in the vicinity of the heating zone within the cooling zone, the aluminium strip into a wave like form toward the moving direction thereof with the radius of curvature smaller than a value represented by - J x X 0.339 R = where, R indicates the radius of curvature, x the summed length of the length of the heating zone and the length of the cooling zone, and y the width of the aluminium strip.

In one embodiment jets of gas may be caused or allowed to impinge on both sides of the aluminium strip to float said strip; and cooling the aluminium strip by the gasses impinging thereagainst in order to float said aluminium strip.

The present invention thus provides a heat treating method which can heat-treat even an aluminium strip, which is liable to produce a longitudinal wrinkle because of a thin materi al, without substantially producing the longitu dinal wrinkle, thus providing products of 130 GB 2 026 043A 1 good quality.

By imparting a wave-form to the strip across the transition from the heating to the cooling zone such that the radius of curvature of said portion is made smaller than the value represented by X X 0.339 R = - y3 (where, x is the sum of the length of the heating zone and the length of the cooling zonr, and y is the width of the aluminium strip.) The antibuckling stress of the aluminium strip becomes greater than the thermal stress produced in the aluminium strip. Accordingly, even if the aluminium strip is heattreated, no longitudinal wrinkle that may materially diminish the value in goods of aluminiurn strip is produced in the aluminium strips.

Following is a description by way of example only and with reference to the accompanying drawings of methods of carrying the in- vention into effect.

In the drawings:- Figure 1 is a schematic longitudinal sectionai view of a heat treating apparatus; Figure 2 is a graphic representation showing changes in temperature of the aluminium strip; Figure 3 is a graphic representation showing a state wherein a thermal stress is produced in the aluminium strip; (in Figs. 1 through 3, corresponding parts therebetween are all shown symmetrized in position. ) Figure 4 is an enlarged sectional view taken on line IV-IV; Figures 5 through 7 are enlarged illustra- tions of essential portions in Figs 1 through 3, respectively; Figure 8 is a sectional view of assistance in explaining the dimensions of a section of the wavy motion; Figure 9 is a schematic perspective view showing a state wherein the aluminium strip is paid off and rewound; Figure 10 is a graphic representation showing the relationship between the radius of curvature and antibuckling stress of the aluminium strip; Figure 11 is a view similar to Fig. 5 showing a different form of embodiment; and Figure 12 is a perspective view showing a state wherein wrinkles are produced in prior arts.

Referring now to Fig. 1, there is shown a heat treatment apparatus 1 which comprises a heating apparatus 2 and a cooling apparatus 14. First, the heating apparatus 2 will be described. This heating apparatus 2 is shown in longitudinal section in Fig. 4.

A furnace wall 3 is designed to form a heat shielding between the interior and exterior 2 GB2026043A 2 thereof in a known manner. The furnace, wall 3 is partly provided with an entrance port 4 and a reception port 5. An aluminium strip 6 is inserted through the entrance port 4 and reception port 5 as shown. Plenum chambers 7, 7 are provided in a space interiorly of the furnace wall 3. These plenum chambers 7, 7 are located opposedly in position through which aluminium strip 6 passes. On the sur- faces opposed to each other in the plenum chambers 7, 7 there are disposed a plurality of gas blowing nozzles in a known manner. Further, at the ends of the surfaces opposed to each other in the plenum chambers 7, 7 there are provided sections of the wavy motion 7a and 7a, which will be later described in detail. The furnace wall 3 has a circulation fan 8 mounted thereon. A conduit 9 has one end communicated with the circulation fan 8, and the other end being communicated with the plenum chamber 7. Further, a burner 10 is disposed internally of the furnace wall 3. Frontwardly of the entrance port 4 there is disposed a guide roll 11 for guiding the aluminium strip 6 towards the entrance port 4 in a stabilized fashion.

Next, the cooling apparatus 14 will be described. The cooling apparatus 14 is composed of plenum chambers 15, 15, provided with a section of the wavy motion 1 5a, a blower 16, a conduit 17, and the like, similarly to the abovementioned heating apparatus 2 with the exception of provision of the furnace wall for the heat shielding, burner, and the like, as in the heating apparatus 2. A discharge port 18 for the strip 6 is provided between the plenum chambers 15, 15. Rearwardly of the discharge port 18, there is provided a let off roll 19 for delivering the aluminium strip 6 in a stabilized fashion.

Details of wavy motion sections 7a, 1 5a in the plenum chambers 7, 15, respectively, will be explained with reference to Fig. 5. First, the section of wavy motion 7a in the plenum chamber 7 has nozzle plate members 21 and static pressure pads 22 opposed to the aluminium strip 6 to be inserted. The width of these nozzle plate members 21 and static pressure pads 22, namely, the length perpen- dicular to the paper surface in Fig. 5, is the same as or greater than the width W (see Fig. above changes as shown in Fig. 2 by way of 9) of the aluminium strip 6. The nozzle plate one example. (The state of change in tempera member 21 has a plurality of nozzles disposed tures in the vicinity of the boundary between thereon so as to jet gases within the chamber the heating zone 25 and the cooling zone 26 7 toward the aliminium strip 6. Similar to 120 is shown in detail in Fig. 6.) Dimensions of well-known static pressure pads, the static various members are indicated hereinafter.

pressure pad 22 has ports 23, 23 of the The dimension of the aluminium strip is 0.3 t length which is the same as or greater than X 2000 W; the length from the guide roll the width of the aluminium strip 6, so that the 11 to the entrance port 4 is 2 m; the length gases within the plenum chamber 7 are jetted 125 of the heating zone 25 and cooling zone 26 is from the ports 23, 23 toward the aluminium 13 m; and the length from the discharge port strip 6. 18 to the let off roll 19 is 2 m. Dimensions of The wavy motion section 15a in the plenum various portions in the wavy motion sections chamber 15 has also nozzle plate members 7a and 1 5a are indicated in connection with and static pressure pads similar to the wavy 130 Fig. 8 as follows: A = 250 mm, B = 1,200 motion section 7a in the plenum chamber 7 as previously described. In view of fuction, the structure of these nozzle plate members and static pressure pads is similar to that of those in the above-mentioned plenum chamber 7, and therefore, like parts bear like reference numerals used in the above-mentioned plenum chamber 7 so that double description will not be made.

In the following, the operation will be explained. An aluminium strip 6a wound around a pay off reel as shown in Fig. 9 is paid off as indicated by the arrow 30 in a known manner. The thus paid off aluminium strip 6 passes through various known devices, after which it is inserted through the heat treatment apparatus 1. The aluminium strip 6 issued from the heat treatment apparatus 1 passes through various known devices, after which it is wound around the rewind reel as shown at 6b.

In a state where the aluminium strip 6 is inserted through the heat treatment apparatus as previously mentioned, the burner 10, fans 8 and 16 are driven. In the steady condition, the aluminium strip 6 is held floated between the plenum chambers 7, 7, and between the plenum chambers 15, 15 by the hot gases (in the chamber 15, normal air not heated) blown through the nozzles in these chambers. In a portion wherein the aluminium strip 6 is opposed to the wavy motion sections 7a, 15a of the chambers 7, 15, respectively, the strip is curved in the form of a wave toward the moving direction thereof as shown in Fig. 5 in detail. It is noted the fans, chambers and the like in the heating apparatus 2 and cooling apparatus 14 are designed so as to provide functions as described above and to provide characteristics of increasing and decreasing temperatures of aluminium strip 6 as will be described later.

The aluminium strip 6 passing through the heat treatment apparatus 1 in a floating mode is heated by the heating apparatus 2 and then cooled by the cooling appararus 14.

In Fig. 1, a heating zone and a cooling zone are indic@ted at 25 and 26, respectively.

The temperature of the aluminium strip 6 subjected to heat treatment as described 1 1 3 GB2026043A 3 mm, C= 600 mm, D= 50 mm, E= 200 mm, F = approximately 90 mm, and radius of curvature R of the aluminum strip 6 is 1.05 M.

- During the process wherein the aluminium strip 6 is heated and cooled, the thermal stress y (the termal stress in the width of the strip) is produced in the center in the width of the aluminium strip 6 so as to have a large value as shown in Fig. 3, that is, in the vicinity of the boundary between the heating zone 25 and the cooling zone 26. (For details, see Fig. 7) However, the aluminium strip 6 is curved in such a region as previously men- tioned by the wavy motion sections 7a and 1 5a, and hence, the widthwise antibuckling stress of the strip is greater than such thermal stress so that the strip keeps its original shape without being-deformed by the thermal stress.

Fig. 10 shows the relationship between the radius of curvature and antibuckling stress of the aluminium strip having the dimension as described above. In the case of the preceding example, the maximum thermal stress is 2.3 kg /MM2 as shown in Fig. 3. Accordingly, the maximum radius of curvature of 1.05 m from which antibuckling stress capable of withstanding the aforesaid maximum thermal stress is obtained may be found from the graph shown in Fig. 10. It will be noted that in the case the magnitude of thermal stress varies with the type of material or the like, the radius of curvature capable of obtaining the antibuckling stress in correspondence thereto may be found. And various dimensions of the wavy motion sections 7a and 1 5a or jetting pressures of gases issued from the nozzles are selected so that the aluminium strip 6 may be curved into the radius of curvature thus ob- tained.

It has been found that the thermal stress as noted above increases nearly in proportion to the width of the strip 6 and decreases nearly in proportion to the full length of furnace (the sum of the length of the heating zone 25 and the length of the cooling zone 26). It has also been found that the antibuckling stress when the strip 6 is curved is in inverse proportion to a square of the radius of curvature and in inverse to a square of the strip width. Accordingly, it has been found from the foregoing points and various test results that the antibuckling stress capable of withstanding thermal stress produced in the strip may be obtained by setting the radius of curvature R of the aluminium strip 6 to a value smaller than that obtained by R= v -Y-1 --- where, x is the sum of the length of the heating zone 25 and the length of the cooling zone 26, and y is the width of aluminium strip.

It is preferable that a position at which wavy motion is applied to the aluminium strip 6 in the aforementioned wavy motion section corresponds to a position at which a great thermal stress is produced in the aluminium strip 6. For example, where the position at which a great thermal stress is produced, in Fig. 3, is in the inner part of the cooling zone, the position at which the strip is curved is also desirable in the inner part of the cooling zone accordingly.

Next, Fig. 11 shows a further embodiment of the present invention, in which static pres- sure pads 22e in wavy motion sections 7ae, 1 5ae of plenum chambers 7e, 15e, respectively, are differently positioned.

Since the static pressure pads 22e are positioned as just mentioned, an aluminium strip 6e may be moved curved as shown to obtain a great antibuckling stress similar to the preceding embodiment.

It is noted that parts shown in Fig. 11 considered identical or equal in structure to those shown in Fig. 5 in function bear like reference numerals in Fig. 5 with an alphabet 11 e- affixed thereto, and double explanation will not be made.

It should be noted that the radius of curva- ture determined in the case the aluminium strip is curved during the process of moving the aluminium strip as described above may be set to a value smaller than the value R as previously mentioned, in the case of the ra- dius of curvature set to a small value as just mentioned, even if wrinkles are produced in the strip due to thermal stress produced therein during the process of moving the aluminium strip, the strip remains curved so as to have such a small radius of curvature, and as a consequence, it is possible to smooth the thus produced wrinkles to the extent that the wrinkles disappear.

While, in the embodiments so far de- scribed, the plenum chambers have been used in the heating apparatus and cooling apparatus, it should be understood that in place of these plenum chambers, other suitable structures may also be employed in order to float the aluminium strip and to apply thereto heat treatment such as heating or cooling.

Claims

1. A method for the heat treatment of aluminium strips comprising the steps of passing an aluminium strip in a floating mode through a heating zone in a floating mode through a cooling zone, characterised by the steps of curving, in a position in the vicinity of the heating zone within the cooling zone, the aluminium strip into a wave- like form toward the moving direction thereof with the radius of curvature smaller than a value represented by 4 GB 2 026 043A 4 XX.339 0 R = C -y3 where, R indicates the radius of curvature, x the summed length of the length of the heating zone and the length of the cooling zone, and y the width of the aluminium strip.

2. A method as claimed in claim 1 further including the steps of causing or allowing jets of gas to impinge on both sides of the aluminium strip to float said strip; and cooling the aluminium strip by the gases impinging thereagainst in order to float said aluminium strip.

3. A method as claimed in claim 2 wherein the jets of gas impinging upon the surface of the strip are applied as alternate weak and strong jet along the direction of travel thereof on both the first and the second surface of the strip; the position of the strong jets being staggered on opposite sides of the strip, the arrangement being such that a strong jet impinges on a first side of the strip substantially in register with a wak jet impinging on the second side thereof thereby imparting a wave like form to the strip passing said jets.

4. A method as claimed in claim 3 where- in the weak jet of gases is formed by applying a jet of gases to the aluminium strip while the gases being widely distributed, said gases being debouched from numerous perforations widely distributed in a plate member disposed in parallel to the direction of movement of the aluminium strip, and wherein each of said strong jets of gas is formed by a gas stream debouching from static pressure pads directed toward said strip surface.

5. A method as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

Printed for Her Majestys Stationery Office by Burgess & Son (Abingdon) Ltd-1 980. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.

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